The objective of our studies is to analyze both the structure and forces stabilizing the normal periodic array of membranes in the myelin sheath of nerves, and to characterize the mechaisms by which structural traNsitions occur. Well-defined transitions of the membrane array to compacted and swollen states are beng characterized by X-ray diffraction and electron microscopy. Particle segregations caused by compaction are being studied by freeze-fracture microscopy. The changes in the balance of forces between adjacent bilayers that underlie both membrane compaction and lipid flocculation are under investigation through studies on myelin lipids. Alterations in the structure and dynamic properties of myelin membranes after purification are being assessed. Techniques are being developed to trap transitional structural states by freezing at low temperature for study by correlated X-ray diffraction and freeze-fracture.